This proposal seeks to technically develop and clinically evaluate microwave thermography, a relatively new, safe, non-invasive method in the area of diagnostic radiology. The development and evaluation will be applied to the detection of breast cancer. The frequencies to be used are 1, 2, 3, and 6 GHz, in continuation of previous work indicating true positive detection rates superior to those of infrared thermography and comparable to those of mammography. At these frequencies microwave thermography can sense temperature changes approximately 0.1 degrees C at depths of several cm with resolution of approximately 1 sq.cm. The techniques to be developed or investigated are (a) reflection-compensating radiometry, which measures both temperature and emissivity; (b) multimode antennas, which form beams of different resolution; and (c) correlation interferometry. The clinical evaluation programs include clinical trials of these techniques; and trials detected toward determination of (a) the most effective frequency, (b) the ability of microwave thermography to detect small tumors; (c) the ability of microwave thermography to detect tumors in young women; (d) whether microwave thermography may be useful in a screening program which reduces the number of women exposed to X-rays; and directed toward (e) construction, for the first time, of microwave images to be compared with other diagnostic images.